Windows threads - how to make a method a thread function in windows?

Question

I can't pass a pointer to method to the CreateThread function, of course. What should I do?

possible duplicate of [Simple example of threading in C++](http://stackoverflow.com/questions/266168/simple-example-of-threading-in-c) — George Stocker, Jun 09 '11 at 16:19
Use CreateThread with caution, as it doesn't initialize the C (and possibly the C++) runtime for the new thread. — Jörgen Sigvardsson, Jun 09 '11 at 22:55

score 7 · Answer 1 · answered Jun 09 '11 at 16:02

If using a class, some pattern like this usually works well:

.h

static UINT __cdecl StaticThreadFunc(LPVOID pParam);
UINT ThreadFunc();

.cpp

// Somewhere you launch the thread
AfxBeginThread(
    StaticThreadFunc,
    this);  

UINT __cdecl CYourClass::StaticThreadFunc(LPVOID pParam)
{
    CYourClass *pYourClass = reinterpret_cast<CYourClass*>(pParam);
    UINT retCode = pYourClass->ThreadFunc();

    return retCode;
}

UINT CYourClass::ThreadFunc()
{ 
    // Do your thing, this thread now has access to all the classes member variables
}

score 5 · Answer 2 · answered Jun 09 '11 at 16:04

I often do this:

class X {
private:
    static unsigned __stdcall ThreadEntry(void* pUserData) {
        return ((X*)pUserData)->ThreadMain();
    }

    unsigned ThreadMain() {
         ...
    }
};

And then I pass this as user data to the thread creator function (_beginthread[ex], CreateThread, etc)

score 4 · Answer 3 · answered Jun 09 '11 at 15:55

The most common way is to create a Thread class that has a run() method and a start() method (these names borrowed from the Java Thread class). run() is a pure virtual that you overload in a class derived from Thread to do the actual work. The method start() internally calls CreateThread passing the this pointer via reinterpret_cast to void*. The Thread class has also a threadEntryPoint() static function that you pass to CreateThread. In threadEntryPoint() you do a reinterpret_cast back to Thread* and then call run() on it.

If there's one situation in which you just want a method of another class to be executed on a separated thread (without having to inherit from the Thread class) you can create a Thread-derived class that receives a pair object+method pointers in the constructor, and calls them in run(). To ease things up, make this derived class a template. Also take a look on boost for functor adaptors.

thanks. as i understood, i only nedd to add one static function to my class and one method to start, threadEntryPoint functionality will be realized in the statiс method. — KOLANICH, Jun 09 '11 at 16:03
Yes, if you want to do this once-only it's as simple as that. If you want to reuse it in other places, it'd be better to isolate the code in a separated class. — Fabio Ceconello, Jun 09 '11 at 16:08

score 1 · Answer 4 · answered Jun 09 '11 at 16:06

1

CreateThread won't take a pointer to a member function. You can wrap the member function in a static function which takes the object pointer through lpParameter.

answered Jun 09 '11 at 16:06

pepsi

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score 1 · Answer 5 · answered Sep 13 '11 at 11:33

CreateThread's lpStartAddress is of type DWORD (WINAPI *PTHREAD_START_ROUTINE)(LPVOID lpThreadParameter) and this is incompatible with the member function since the member function has an implicit this pointer in its signature. So create a static function and pass the class pointer as the argument to the thread function.

score -1 · Answer 6 · answered Jun 09 '11 at 16:05

-1

If you are talking about Native CreateThread Method you would probably need to do following

CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)&MyThreadProc,NULL,NULL,&threadId);

Where your callback method is defined as

void MyThreadProc()
{
}

answered Jun 09 '11 at 16:05

crypted

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3

You don't want to do this - the cast here is a problem: generally speaking, you should never cast a function just to make things work. Instead you should pass MyThreadProc without a cast, and then change void MyThreadProc() to be DWORD WINAPI MyThreadProc(LPVOID), which is what CreateThread is expecting. Passing a function with a different number or type of params or calling convention than an API is expecting can lead to a messed-up stack. – BrendanMcK Jun 09 '11 at 22:05

Windows threads - how to make a method a thread function in windows?

6 Answers6